In recent years, in mobile terminals and other communication devices, use has been made of an acoustic wave element for a duplexer for filtering signals transmitted and received to and from an antenna. An acoustic wave element is configured by a piezoelectric substrate and an excitation electrode which is formed on a major surface of the piezoelectric substrate. The acoustic wave element utilizes the feature that an electrical signal and a surface acoustic wave can be converted with each other due to the relationship between the excitation electrode and the piezoelectric substrate.
The duplexer for example forms a receiving filter and transmission filter by using a plurality of acoustic wave elements (see Japanese Patent Publication No. 2007-214902A). The duplexer combines a plurality of acoustic wave elements to set pass bands of the receiving band and transmission band.